The present invention relates generally to bicycles, and more particularly to a method of manufacturing a hollow, monocoque carbon fiber bicycle frame which is lightweight, durable, and relatively inexpensive to manufacture and finish.
The fabrication of bicycle frames from fiber reinforced polymer composites is well known in the prior art. According to prior art fabrication methodology, these composite bicycle frames are typically constructed by first pre-forming the elongate, composite members thereof, and then interconnecting these members with composite joints. For example, in one commonly practiced prior art composite bicycle frame fabrication process, separate top tube, down tube, and seat tube members are initially formed from fiber reinforced polymer composites, and subsequently placed into a common fixture. The placement of these members into the fixture maintains their desired orientations while they are connected to each other by forming interconnecting joints therebetween with additional fiber reinforced polymer composite material.
As will be appreciated by those skilled in the art, though this particular prior art fabrication methodology provides a bicycle frame which is lightweight and durable, it is extremely time consuming and expensive. The high amount of labor and resultant expense is attributable to each of the interconnecting joints having to be individually fabricated by hand, and the need to conduct extensive finishing operations upon the frame to provide the same with the desired smooth, properly contoured outer surface. Thus, although the prior art has recognized to a limited extent the benefits of providing a lightweight and durable bicycle frame, the known fabrication methodologies for such frames have been time consuming and cost ineffective.
In recognition of the deficiencies of prior art fabrication methodologies which employ the use of fiber reinforced polymer composite materials, Applicant has developed the composite bicycle frames and associated manufacturing methodologies described and claimed in the above-listed parent applications. These improved methodologies facilitate the minimization or elimination of the prior art steps needed to provide the interconnection of the various frame members or components to each other, and provided the desired smooth overall finish to the bicycle frame, thus substantially reducing the amount of labor involved in the manufacturing process and hence reducing the associated costs.
More particularly, Applicant's previous methodologies involve the placement of an elongate, flexible and expandable bladder covered with a polymer impregnated fiber material into a first mold section, and subsequently mating a second mold section to the first mold section so as to define a cavity having a desired frame shape through which the bladder covered with the polymer impregnated fiber material is extended. The polymer impregnated fiber material is then heated, with the bladder being inflated so as to cause the material to substantially conform to the shape of the cavity. The frame tube fabricated from this process includes at least a top tube portion and a down tube portion, and is formed entirely from a single, continuous section of the fiber reinforced polymer composite.
Though this methodology provides the aforementioned advantages over the prior art, the use of a non-rigid bladder therein gives rise to a susceptibility for the material to flow into unknown folds and/or wrinkles in the bladder during the pressurization thereof. As will be recognized, the flow of material into any such folds and/or wrinkles during the fabrication process results in undesirable inconsistencies in the wall thickness of the completed frame tube. The present invention addresses this particular shortcoming by providing a similar fabrication methodology which employs the use of a semi-rigid core or bladder to allow for better control of the internal wall surface texture and wall thickness of the resultant frame tube due to the absence of any unknown folds and/or wrinkles in the core for the material to flow into during the process of pressurizing the core. As in Applicant's previous fabrication methodologies, the present method also provides an absolutely continuous layer of fiber material about the entire frame tube where needed as opposed to a simple overlap of material as described in many prior art fabrication methodologies. These and other advantages attendant to the present invention will be discussed in more detail below.